Mechanical disconnect dual-sided interlocking teeth

ABSTRACT

A disengagement/disconnect assembly for disengaging a generator from a gear box may include an inner ball screw having an angled threading on an outer surface thereof and surrounding and operatively engaged to a rotating generator drive shaft to cause rotation of the inner ball screw. The inner ball screw may be attached to an engagement member having undercut and interlockable teeth engaged to corresponding teeth of an engagement member of the gear box. An outer ball screw may surround and normally rotate with the inner ball screw. A helical ball track may be formed between the inner and outer ball screws. A brake may be provided for slowing or stopping rotation of the outer ball screw so that the inner ball screw rotates relative to the outer ball screw along the ball track and slides axially away from the gear box thereby disengaging the generator from the gear box drive shaft.

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus and methods fordisengaging generators and other rotating machines from a prime moverand, more particularly, to apparatus and methods of disengaging anaircraft generator from an engine or gear box to prevent damage to theengine or gear box.

In the aerospace industry, aircraft receive electric power fromgenerators. The generators may be coupled to the main engine or toauxiliary power units through a gear box. Known designs of generatorshave a generator drive shaft that includes some kind of shear sectionthat is based on safe operational capability of the gearbox. In theevent that the generator malfunctions, this shear section operates andprotects the gear box from continuing to rotate under an unacceptableload from a malfunctioning generator that may have stopped rotating. Forconstant speed generators, the design of the shear section is notdifficult—it is easy to design a shear section to meet one speed.However, with the evolution of variable frequency generators (VFG),where failure can occur over a range of speeds, it is rather difficultto design a shear section that can protect the gear box regardless ofthe multiple possible speeds of the generator.

It is therefore useful that some other means should be incorporated intothe design of the generator that would help protect the gear box. If,for example, there is a minor fault with the generator and it is notproducing any power but rather is rotating like a load on the gear box,it is desirable that the generator be de-coupled from the gear box.

It is also useful that such a protection means should not interfere withproper engagement of the generator with the gearbox irrespective ofwhether a generator shaft is producing load on the gearbox oralternatively when the gearbox may be producing mechanical load on thegenerator shaft.

As can be seen, there is a need to disengage the generator from the gearbox as needed when the generator malfunctions. Furthermore, there is aneed to have such a disengaging mechanism that is re-settable by theoperator or maintenance personnel of the aircraft when the problem withthe generator is fixed or addressed. It is also required that thedisconnect mechanism not disengage unnecessarily and not inadvertentlyengage when disconnected.

SUMMARY OF THE PRESENT INVENTION

In one aspect of the present invention a dis-engageable generator drivesystem comprises a first engagement member coupled to a generator, and asecond engagement member coupled to an engine. The engagement membershave a plurality of circumferentially disposed teeth. The teeth have adistal circumferential width at their distal ends and a proximalcircumferential width at their proximal ends wherein the distalcircumferential width is greater than the proximal circumferentialwidth.

In a further aspect of the invention a disengagement assembly fordisengaging a generator from an engine comprises an axially displaceableengagement member. The engagement member has a plurality ofcircumferentially disposed teeth. The teeth have a distalcircumferential width at their distal ends and proximal circumferentialwidth at their proximal ends wherein the distal circumferential width isgreater than the proximal circumferential width.

In another aspect of the invention a method of driving a generator withan engine comprises the steps of Interlockingly engaging the engine withan inner ball screw having an angled threading on an outer surfacethereof, engaging the inner ball screw with an outer ball screw thatrotates with the inner ball screw, including an angled ball trackbetween the inner ball screw and the outer ball screw on which a ballbearing travels, and actuating a brake to slow or stop rotation of theouter ball screw so that the inner ball screw rotates relative to theouter ball screw along the ball track and slides axially away from theengine thereby disengaging the generator from the engine..

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a drive system wherein a generator is inits normal state engaged with an engine in accordance with theinvention;

FIG. 2 is a sectional view of the disengagement assembly of FIG. 1wherein the generator is disengaged from the engine in accordance withthe invention;

FIG. 3 is a perspective view of a generator-side engagement member inaccordance with the invention;

FIG. 4 is a perspective view of an engine-side engagement member inaccordance with the invention;

FIG. 5 is a graphical representation of teeth and recesses of theengagement members of FIGS. 3 and 4 in accordance with the invention;

FIG. 6 is a graphical representation of teeth and recesses of theengagement members of FIGS. 3 and 4 in accordance with the invention;

FIG. 7 is another graphical representation of teeth and recesses of theengagement members of FIGS. 3 and 4 in accordance with the invention;

FIG. 8 is a graphical representation of teeth and recesses of theengagement members of FIGS. 3 and 4 in a disengaged state in accordancewith the invention; and

FIG. 9 is a flow chart showing a method in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

The present invention generally provides a disengagement assembly for arotating machine, such as an aircraft generator, for disengaging thegenerator from an engine or gear box. Typically, the drive shaft of thegenerator may be rotating and operatively engaged to the drive shaft ofthe gear box. When the generator is not working properly, for example inan aircraft, the disengagement assembly may allow a pilot to disengagethe generator from the gear box. The disengagement assembly may be amodular or standalone assembly having its own housing separate from thehousing of the generator, or alternatively the disengagement assemblymay be subsumed within the housing of the generator. The disengagementassembly may be used in aircraft and may be re-settable manually on theground after repair of the generator.

In contrast to the prior art, which does not use interlocking engagementteeth, the disengagement assembly of the present invention may utilize aball screw mechanism to provide a desired axial positioning of novelengagement teeth which maintain an interlocking relationship with oneanother irrespective of direction of torque application during properoperation of the generator. The interlocking teeth may disengage fromone another in the event of a malfunction of the generator. In furthercontrast to the prior art, in which the disconnect mechanism has toself-destruct in order to function; the disengagement assembly of thepresent invention may be resettable and reusable.

As seen from FIGS. 1 and 2, a generator drive system 10 may be providedwith a disengagement assembly 11 for disengaging a variable frequencygenerator 12 from a gear box 13 of a prime mover or engine 14. Thedisengagement assembly 11 may comprise a rotatable inner ball screw 16that has angled threading 16-1 on an outer surface 16-2 of inner ballscrew 16.

Since inner ball screw 16 may be hollow, inner ball screw 16 maysurround and may be operatively engaged to a generator drive shaft 18 sothat the rotation of generator drive shaft 18 on an axis 19 may causerotation of inner ball screw 16. In this regard, there may be radiallyprotruding splines 20 between the surface of generator drive shaft 18and an inner surface 16-3 of inner ball screw 16. The splines 20 oranother suitable structure may serve to transfer rotational force of thegenerator drive shaft 18 to inner ball screw 16.

Inner ball screw 16 may have an engagement member 22, at an end distalto the generator 12. This engagement member 22 may be normally engagedto a corresponding engagement member 24 which may be connected to thegearbox 13 or optionally to the engine 14 if a gearbox is not utilized.

Disengagement assembly 11 may also include an outer ball screw 26 whichmay surround and may normally rotate with inner ball screw 16. As seenin FIG. 2, outer ball screw 26 may have associated with it one or moreballs 28, called ball bearings, that travel on an angled ball track 30that exists between the inner ball screw 16 and outer ball screw 26. Inone exemplary embodiment, there may be between approximately five andseven such balls depending upon the design requirement. The angled balltrack 30 may be formed from threading 16-1 on the inner ball screw 16and outer threading 26-1 formed on the outer ball screw 26. The factthat the ball track 30 is angled means that ball track 30 has some axialcomponent rather than simply being a series of revolutions around innerball screw 16.

Disengagement assembly 11 may also include a brake 38 that may becapable of slowing or stopping rotation of outer ball screw 26. When thebrake 38 slows or stops rotation of outer ball screw 26, since normallyinner ball screw 16 rotates together with outer ball screw 26, thisslowing or stopping of the rotation of outer ball screw 26 may causeinner ball screw 16 to rotate relative to outer ball screw 26 along balltrack 30 and simultaneously slide axially away from the engine 14thereby disengaging the generator 12 from the engine 14. When inner ballscrew 16 slides axially away from engine 14, inner ball screw 16 may besliding on generator drive shaft 18, and more precisely on splines 20between the surface of generator drive shaft 18 and inner surface 16-3of inner ball screw 16.

Accordingly, outer ball screw 26 may be capable of rotation and innerball screw 16 may be capable of both rotation and axial movement. Thebrake 38 may be connected to a solenoid 40 that may be remotelyactuatable by an aircraft pilot when generator 12 malfunctions. Otherarrangements may easily be imagined whereby brake 38 may be controlleddirectly or indirectly with other mechanisms.

Referring now to FIGS. 3 and 4 it may be seen that the engagement member22 may include interlockable teeth 22-1 and the corresponding engagementmember 24 of the gear box drive shaft adaptor 14 may also includeinterlockable teeth 24-1 that mate with the teeth 22-1. In an exemplaryembodiment shown in FIG. 3 the teeth 22-1 may be positionedcircumferentially around the engagement member 22. It may also be notedthat while an exemplary number of eight of the teeth 22-1 are shown inFIG. 3, each of the teeth 22-1 covers only about 15 degrees of angulardisplacement around the circumference of the engagement member 16.Recesses 22-2 between the teeth 22-1 cover a larger portion of thecircumference than the teeth 22-1. Each of the recesses 22-2 may coverabout thirty degrees of angular displacement of the circumference. Inthis regard it may be seen that recesses 22-2 may be about twice as wideas their respective adjacent teeth 22-1. The engagement member 24 shownin FIG. 4 may also be provided with similar teeth 24-1 and recesses 24-2which may interconnect and interlock with the teeth 22-1 and recesses22-2 of the engagement member 22.

Referring now to FIGS. 5, 6 and 7, a novel relationship of the teeth22-1 and 24-1 and the recesses 22-1 and 24-2 may be appreciated.Referring particularly to FIG. 5, consider first a configuration ofengagement member 22. Each of the teeth 22-1 may be formed with aproximal end 22-3 smaller than a distal end 22-4. In other words, eachof the teeth 22-1 may be formed with a profile that resembles atruncated pyramid. Each of the recesses 22-2 may be formed with aproximal end 22-5 larger than a distal end 22-6. Tooth sides 22-7 may beformed at an angle A relative to an axis 19 of the generator 12 ofFIG. 1. Tooth sides 22-8 may be formed at the angle B relative to theaxis 19.

The engagement member 24 may have its teeth 24-1 and its recesses 24-2formed in the same manner as the teeth 22-1 and the recesses 22-2 of theengagement member 22.

FIGS. 5, 6 and 7 are intended to provide a readily understandablegraphical representation of the interlocking nature of the teeth 22-1and 24-1 and the recesses 22-2 and 24-2. As such FIGS. 5, 6 and 7 maynot show their respective objects in scale. In an actual exemplaryembodiment of the invention, the angles A and B may be equal inmagnitude and opposite in direction relative to the axis 19. The anglesA and B may be between about three degrees and about one degree. Each ofthe teeth 22-1 and 24-1 may have a height H of about 0.050 inch to about0.150 inch. In a typical exemplary embodiment the engagement member 22may have a diameter of between about 2 inches to about 3 inches. In thiscontext each of the recesses 22-2 and 24-2 may have a distal width ofbetween about 0.50 inch and 0.80 inch. Each of the teeth 22-1 and 24-1may have a distal width of about 0.25 inch to about 0.40 inch.

Referring now particularly to FIG. 6, it may be seen how the teeth 22-1and 24-1 interact with one another when the engine 14 or its gearbox 13may apply a torque load to the generator 12, i.e. when engagement member24 drives engagement member 22. FIG. 6 shows a direction of rotationarrow 62 portraying a counterclockwise rotation of the generator 12 andthe engine 14. Left-hand sides 24-7 of each of the teeth 24-1 may engagewith and produce circumferential force on right-hand sides 22-8 of theteeth 22-1. Because each of the teeth 22-1 and 24-1 may be shaped astruncated pyramids, the sides 24-7 and 22-8 of the teeth 24-1 and 22-1may engage with one another to produce an axial force. In other words,the engagement member 22 may be drawn toward engagement member 24 in anaxial direction.

As torque load increases, the axial force increases correspondingly. Ina typical aircraft generating system rotational speeds of 24,000revolutions per minute (rpm) may develop. Torque loads of 300foot-pounds may also be encountered, increasing torque and speed oftenresults in increased vibration. Increased vibration may increase a riskthat the engagement members 22 and 24 may inadvertently release from oneanother. The novel arrangement of interlocking angled teeth 22-1 and24-1 may provide desirable axial force that may increase with increasingtorque. Thus the risk of inadvertent disengagement may be reduced.

Referring now particularly to FIG. 7, it may be seen how the teeth 22-1and 24-1 interact with one another when the generator 12 applies atorque load to the engine 14. FIG. 7 shows a direction of rotation arrow62 portraying a counterclockwise rotation of the generator 12 and theengine 14. Left-hand sides 22-7 of each of the teeth 22-1 may engagewith and produce circumferential force on right-hand sides 24-8 of theteeth 24-1. As described with respect to FIG. 6, the teeth 22-1 and 24-1may engage with one another to produce an axial force. In other words,the engagement member 22 may be drawn toward engagement member 24 in anaxial direction.

Considering both FIGS. 6 and 7 it may be seen that irrespective ofwhether the generator 12 is being driven by torque from the engine 14 oris producing torque force on the engine 14, the teeth 22-1 and 24-1 mayremain engaged. Additionally, it may be seen that the teeth 22-1 and24-1 may produce axial force in the presence of torque provided byeither the generator 12 or the engine 14. Thus, the inventive engagementmembers 22 and 24 may provide effective torque transmission under manydifferent operating conditions. For example, during engine start-up thegenerator 12 may be employed as a starter motor. In that case, thegenerator 12 may drive the engine 14, i.e., the engagement member 22 maydrive the engagement member 24. Conversely, during steady-stateoperation of the engine 14, the engine 14 may produce torque load on thegenerator 12 and the engagement member 24 may drive the engagementmember 22. In the event of engine deceleration, the engagement member 22may again drive the engagement member 24.

Referring now to FIG. 8 and back to FIG. 2, it may be seen that uponapplication of the brake 38, the engagement members 22 and 24 may beaxial displaced from one another and thus separated. In such an eventthe engagement members 22 and 24 may slightly rotate relative to oneanother. This slight relative rotation may provide relativedisplacements of the teeth 22-1 and 24-1 relative to one another asshown in FIG. 8. Each of the teeth 22-1 and 24-1 may be angularlydisplaced relative to the recesses 22-2 and 24-2. Each of the recesses22-2 and 24-2 may have a circumferential width greater than that of eachof the teeth 22-1 and 24-1. In the case of the exemplary embodimentdescribed herein, each of the recesses 22-2 and 24-2 may be twice aswide as the respective teeth 24-1 and 22-1. However, it should notedthat the distal width of the recesses 22-2 and 24-2 need only be greaterthan the distal width of the teeth 22-1 and 24-1 in order to allow foroperations of the disengagement assembly 10. In other words, the distalends 22-6 and 24-6 of the recesses 22-2 and 24-2 may be wider than thedistal ends 22-4 and 24-4 of the teeth 22-1 and 24-1. The teeth 22-1 and24-1 may require only a few degrees of angular displacement relative toone another before the teeth 22-1 and 24-1 may freely move axiallyrelative to one another.

The disconnect assembly 11 may also include a locking mechanism 42 forlocking inner ball screw 16 in place after inner ball screw 16 has movedlaterally/axially away from the engine 14 to disengage generator 12 fromthe engine 14 or its gearbox 13.

As seen in FIG. 1, one example of lock mechanism 42 is shown whereby thelock may be a simple key or pin 42-1 whose bottom is urged upmomentarily by a slanted back shoulder 16-4 at a proximal end of innerball screw 16, and then falls back down once slanted back tooth 16-4passes key 42-1, thereby ensuring that inner ball screw 16 is held inplace by lock 42 (i.e. cannot reverse direction) until key 42-1 isre-set. The re-setting of lock 42 may be performed manually by anoperator which may be achieved manually on the ground by releasing lock42 such as by causing key 42-1 to be lifted. This may allow springs 43to push inner ball screw 16 back to its normal position engaged to theengine. Accordingly, when the lock 36 is later manually released, innerball screw 16 automatically may revert to its engagement position byrotating through ball track 30 in a reverse direction and slidingaxially. The generator 1 2 may be then re-engaged to the gear box 13 orthe engine 14 for future normal operation.

Although as seen from FIGS. 1-2, the entire disconnect mechanism 11 maybe outside of a housing 12-1 of generator 12 and may have its ownhousing (not shown), it is also contemplated by the present inventionthat in certain embodiments disengagement/disconnect assembly 11 mayalso be subsumed within and utilize housing 12-1 of generator 12.

Referring now to FIG. 9, which is a flow chart, it may be seen that thepresent invention also envisions a method 900 of driving a rotatingmachine such as a variable frequency generator with an engine anddisengaging the generator in the event of a malfunction of thegenerator. In a step 902, engagement members may be interlockinglyengaged (e.g., the engagement members 22 and 24 may be engaged withinterlocking of the teeth 22-1 and 24-1 into the recesses 22-2 and24-2). In a step 904, torque may be applied to the engagement members toproduce an axial force (i.e., angled sides 22-7, 22-8, 24-7 and 24-8 mayproduce axial force upon application of torque on the engagement members22 and 24). In a step 906, a malfunction of the generator may bedetected. In a step 908 an axial withdrawal mechanism may be activated (a pilot may activate a solenoid 40 to apply a brake 38 and produce axialmotion of the engagement member 22 through operation of a ball-screwassembly). In a step 910, angular and axial displacement between theengagement members may provide for disengagement of the engine from thegenerator (e.g., the inner ball screw 16 may produce axial force on theengagement member 22 sufficient to overcome the axial force produced bythe angled sides of the teeth 22-1 and 24-1)

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A disengageable generator drive system comprising: a first engagementmember coupled to a generator; a second engagement member coupled to aprime mover; the engagement members having a plurality ofcircumferentially disposed teeth; the teeth having a distalcircumferential width at their distal ends and a proximalcircumferential width at their proximal ends; and wherein the distalcircumferential width is greater than the proximal circumferentialwidth.
 2. The drive system of claim 1; wherein the teeth are equallysized and equally distributed circumferentially of their respectiveengagement members; wherein the engagement members are provided withcircumferentially disposed recesses between the teeth; wherein therecesses have sides that are comprised of sides of the teeth; andwherein the recesses have a circumferential width greater than thedistal circumferential width of the teeth.
 3. The drive system of claim1 wherein the teeth have at least one of their sides oriented at anangle of about one degree to about three degrees relative to an axis ofthe generator.
 4. The drive system of claim 1: wherein the teeth havetwo of their circumferentially opposing sides oriented at an anglerelative to an axis of the generator; and wherein the two sides areoriented at angles that are equal in magnitude and opposite indirection.
 5. The drive system of claim 1 wherein the teeth have aheight between their distal and proximal ends of about 0.050 inch toabout 0.150 inch.
 6. The drive system of claim 1 wherein the recesseshave a circumferential width that is about twice the circumferentialwidth of the distal circumferential width of the teeth.
 7. The drivesystem of claim 1 wherein the engagement members exert axial force onone another in a presence of a torque load on either of the engagementmembers.
 8. The drive system of claim 7 wherein the engagement membersexert axial force on one another irrespective of which of the engagementmembers is a driving member.
 9. A disengagement assembly for disengaginga generator from an engine comprising an axially displaceable engagementmember; the engagement member having a plurality of circumferentiallydisposed teeth; the teeth having a distal circumferential width at theirdistal ends and a proximal circumferential width at their proximal ends;wherein the distal circumferential width is greater than the proximalcircumferential width.
 10. The disengagement assembly of claim 9 furthercomprising: a rotatable inner ball screw having an angled threading onan outer surface thereof, the inner ball screw fixedly connected to theengagement member; an outer ball screw surrounding the inner ball screw;an angled ball track between the inner ball screw and the outer ballscrew; a ball bearing traveling on the angled ball track; and a brakecapable of slowing or stopping rotation of the outer ball screw so thatthe inner ball screw rotates relative to the outer ball screw along theball track and slides axially thereby disengaging an engaged generatorfrom an engine.
 11. The assembly of claim 10 wherein the brake isconnected to a solenoid that is remotely actuatable by a pilot when thegenerator malfunctions.
 12. The assembly of claim 10, also including alock capable of preventing re-engagement of the engine and the generatorprior to elimination of the generator malfunction.
 13. The assembly ofclaim 12, wherein the lock is re-settable.
 14. The assembly of claim 13,wherein springs at a proximal end of the shaft urge the inner ball screwtoward the engine when the lock is reset.
 15. A method of driving agenerator with an engine comprising the steps of: interlockinglyengaging the engine with an inner ball screw having an angled threadingon an outer surface thereof; engaging the inner ball screw with an outerball screw that rotates with the inner ball screw, including an angledball track between the inner ball screw and the outer ball screw onwhich a ball bearing travels; and actuating a brake to slow or stoprotation of the outer ball screw so that the inner ball screw rotatesrelative to the outer ball screw along the ball track and slides axiallyaway from the engine and rotationally displacing the inner ball screwrelative to the engine thereby disengaging the generator from theengine.
 16. The method of claim 15, further comprising preventing theinner ball screw from re-engaging the engine by applying a lock afterthe generator is disengaged form the engine.
 17. The method of claim 16,including re-engaging the generator with the engine by means of thesprings upon re-setting the lock.
 18. The method of claim 15 wherein thestep of interlockingly engaging comprises engaging angled interlockingteeth connected to the generator with angled interlocking teethconnected to the engine.
 19. The method of claim 18, includingmaintaining an axial load on the inner ball screw by urging the innerball screw toward the engine with the angled interlocking teeth whilethe engine and generator are engaged.
 20. The method of claim 15,including remotely actuating a solenoid connected to the brake when thegenerator is malfunctioning.